The invention relates to a system for asymmetrical signal transmission from a pair of transmission devices through a pair of signal paths, each having at least one signal line, and one reference line to a pair of receiver devices, two devices of which have a supply reference potential in common and are coupled to one end of each of the two signal paths, and the other two devices of which have a further supply reference potential in common and are coupled to the other end of each of the two signal paths. The invention also relates to a transmission and receiver device for use in such a system.
The system may be realized when interconnecting electronic devices -- such as, for example, a TV receiver to peripheral equipment (e.g. a video recorder, a video disc player, a TV monitor, etc.) -- in accordance with the European standard ratified on 7 July 1982 and published by the European Committee for Electro-technical Standardization (CENELEC) in the report EN 50049 "Domestic or similar electronic equipment interconnection requirements: peritelevision connector", of December 1983. The plugs and sockets as defined by this standard enable the use of signal paths separated as to signal type. In addition, a sufficient number of connections is reserved for audio and video signals to realize asymmetrical twotraffic along the audio and video signal paths. The transmission cross-talk can thereby be reduced to a minimum. In addition, the asymmetrical transmission limits the number of lines per signal path: thus, for n signals only (n+1) lines are required per signal path (n signal lines and one common reference line), whereas 2n lines are always required in the case of a balanced signal transmission.
In practice, it often occurs that several transmission and/or receiver devices are accommodated in one apparatus. Thus the audio and video demodulator circuits of a TV receiver may apply audio and video signals to, for example, a TV monitor and consequently function as transmission devices. Conversely, for example, a video recorder or video disc player may apply audio and video signals to the audio and video processing and reproducing devices of a TV receiver, which devices thus function as receiver devices.
For practical reasons, the several devices of one apparatus are connected to one common supply reference potential. When interconnecting two such apparatuses, a parallel arrangement of the reference lines of two or more different signal paths is, however, brought about in each apparatus through the connections to the supply reference potentials. As a result of this parallel arrangement, part of one signal (for example, the video signal) may pass from one (video) signal path into the other signal path (for example, the audio signal path) and vice versa, and may give rise to cross-talk components across the impedance of the relevant lines, hereinafter referred to as line impedance, thereby causing the desired signal to be disturbed.
The preliminary publication "Differential technology in recording consoles and the impact of transformerless circuitry on grounding technique" by Thomas M. Hay, presented at the 68.sup.th AES Convention in Hamburg on Mar. 17-20, 1981, particularly in FIGS. 10-18, shows circuits for suppressing 50/60 Hz supply hum which may be induced in a signal path from transmission to receiver device.